The No5 handguard is simply a modified rear No4 handguard. If you tried a used No4 handguard and it was loose, try to get a "newer" one. It'll be oversize, so it'll need fitting, but that will ensure (if done right) that it will fit well. You'll need to cut a small length off the front tip, then carve the band groove in the right spot. Did it a few times, fun small woodworking job. Then you stain to match, refinish with linseed oil and voila.
Lou